Lee Westwood was stung by a wasp as he and Colin Montgomerie - in a fine return to form - battled for the lead at the Portugal Masters in Vilamoura.
"It got me a good 'un," said Westwood, lifting his right trouser leg to reveal a big red mark.
"It only hurts when I put my foot down. It's going to be one long hop round the front nine."
The incident came as he and Ryder Cup Captain Montgomerie, without a top ten finish since June last year, both covered the inward half in a four under par 32 to share the lead with Dane Mads Vibe-Hastrup.
Montgomerie is 103rd on The Race to Dubai and 255th in the World Rankings, but he was the faster of the two off the blocks.
The 46 year old Scot hit his approach to nine feet on the tenth, two-putted the long 12th and came out of a fairway bunker to ten feet for another birdie at the 424 yard 14th.
Westwood, fourth on The Race to Dubai and with a chance to go top this weekend, had opened his account on the 11th, chipped close at the next and then both of them chipped close on the 315 yard 15th.
Close to the water with his drive down the long 17th, Westwood lashed a superb wood over the lake onto the green and horseshoed out with his eagle attempt from 15 feet.
Vibe-Hastrup was also out in 32, but that was on the front nine and it meant the trio led by a stroke from a group which included Marc Warren - Montgomerie's partner when Scotland won the World Cup two years ago - and England's Mark Foster.
Defending champion Alvaro Quiros, 20 year old Rory McIlroy, leader of The Race to Dubai, and Alfred Dunhill Links Championship winner Simon Dyson were among the later starters.